A driver system may be applied for driving an LED assembly, the LED assembly may comprise at least one LED. It is well known for the skilled person to drive the LED assembly by means of a power supply providing for example a constant current to the at least one LED.
A prior art driver system is depicted in FIG. 1. In FIG. 1, a driver system 1 comprises a LED assembly 3, a power supply 5 and a LED driver 7. The LED assembly 3 comprises a plurality of LEDs 11. At least one set of the LEDs 11 is formed in a serial LED chain 12 in the LED assembly 3. The LED driver 7 comprises an (e.g. switched mode) current source 8 and a plurality of switches 9. At least one set of the switches 9 is formed in a serial switches chain 10 whereby a parallel switch is provided for each respective LED or LED group. The power supply 5 in this example comprises a fly-back converter 13 and a power factor correction circuit 15.
The power supply 5 is with an input thereof connected to an alternating current (AC) source 14 and is with an output thereof connected to the LED driver 7. The LED driver 7 is with an input connected to the power supply 5 and is with an output connected to the LED assembly 3. At least one of the switches 9 in the LED driver 7 is connected to one of the LEDs 11 or a group of LEDs in the LED assembly 3.
The power supply 5 receives an alternating current (AC) from the AC source 14. The fly-back converter 13 is arranged to convert a (rectified) mains voltage of the power supply 5 into a constant voltage 17 and transmit the constant voltage 17 to the LED driver 7. The power factor correction circuit 15 is arranged to improve a phase relation between the input current and the input voltage in the power supply 5 so as to improve a power factor.
The LED driver 7 receives the constant voltage 17 from the power supply 5.
The current source 8 is arranged to provide a LED drive current 19 to the LED assembly 3. The switches 9 are arranged to switch ON/OFF the LEDs 11 in the LED assembly 3.
The LEDs 11 in the LED assembly 3 are controlled by the respective parallel switches 9. Each LED of the serial LED chain 12 is activated or de-activated by opening or closing of a respective corresponding switch of the serial chain 10.
In the driver system 1, when applying a constant LED drive current, a voltage across the entire LED assembly 3 will vary substantially with the switching ON/OFF of the separate LEDs or groups of LEDs 12 by the switches 10. When no LEDs 12 are ON, the voltage across the entire LED system 3 will substantially drop to zero. When all LEDs 12 are ON, the voltage across the entire LED system 3 will equal the sum of the voltages of each independent LED group 12.
The abovementioned driver system 1 comprising a cascading of two supplies (namely the, e.g. switched mode, power supply and the, e.g. switched mode, current supply that drives the LEDs) may exhibit shortcomings in its dynamic behavior when driving LED assembly 3.
It is desirable to provide an improved driver system.